白黎芦醇对垂体腺瘤GH3细胞的抑制作用

目的 探讨选择性雌激素受体调节剂白黎芦醇对垂体腺瘤GH3细胞中电压依赖性K^ 电流(IK(V))和细胞增殖的影响。方法 不同浓度白黎芦醇作用GH3细胞，应用MTT比色法测定细胞增殖，流式细胞仪检测细胞周期分布，运用全细胞膜片钳技术记录和分析白黎芦醇对GH3细胞中IK(V)的作用。结果 白黎芦醇作用GH3细胞3d后，以浓度效应关系抑制GH3细胞增殖，并使细胞增殖周期中G0／G1期阻滞，S期和G2／M期百分率降低。全细胞膜片钳结果显示，白黎芦醇以浓度和时间效应抑制IK(V)。结论 白黎芦醇抑制GH3细胞增殖可能是通过阻断电压依赖性K^ 通道起作用。提示可应用选择性抗雌激素药物治疗垂体腺瘤。     

白黎芦醇对GH3细胞生长和泌乳素合成分泌的抑制作用及其与雌激素受体的关系

目的探讨白黎芦醇（RE）对垂体腺瘤GH3细胞增殖和泌乳素（PRL）合成分泌的影响，及其与雌激素受体（ERs）的关系。方法RE作用于GH3细胞．用免疫荧光法和Western印迹法测定ERs的表达情况．分别用ELISA法和Western印迹法测定培养基内和细胞内PRL水平，用MTT法测定细胞增殖，同时观察了雌二醇（E2）和特异性雌激素受体激动剂对RE的拮抗作用。结果RE改变ERs表达水平，减少PRL合成分泌，抑制GH3细胞增殖，E2和特异性雌激素受体激动剂对RE有拮抗作用。结论RE通过ERs抑制PRL合成、分泌及细胞增殖，从而发挥抗肿瘤作用，两种效应的信号转导途径不尽相同。     

A transient voltage-dependent outward potassium current in mammalian cerebellar Purkinje cells

Utilizing the single electrode voltage clamp technique applied to rat Purkinje cells (PCs), we have recorded a transient outward voltage-dependent potassium current, I_to. Half maximal values for inactivation and activation were −65 mV and −39 mV, respectively. I_to decays as a single exponential with a time constant of 95 ms and is reduced by 4-aminopyridine. Based on criteria of voltage dependency of activation and inactivation, kinetics of inactivation, ionic selectivity and pharmacologic sensitivity, we have verified a strong resemblance between the typical A current in other neurons, and I_to in PCs. As in other cells, I_to may be important in shaping PC output by modulating intrinsic and extrinsic factors that govern PC firing.     

Inhibitory effect of lamotrigine on A-type potassium current in hippocampal neuron-derived H19-7 cells

PURPOSE: We investigated the effects of lamotrigine (LTG) on the rapidly inactivating A-type K+ current (IA) in embryonal hippocampal neurons. METHODS: The whole-cell configuration of the patch-clamp technique was applied to investigate the ion currents in cultured hippocampal neuron-derived H19-7 cells in the presence of LTG. Effects of various related compounds on IA in H19-7 cells were compared. RESULTS: LTG (30 microM-3 mM) caused a reversible reduction in the amplitude of IA. The median inhibitory concentration (IC50) value required for the inhibition of IA by LTG was 160 microM. 4-Aminopyridine (1 mM), quinidine (30 microM), and capsaicin (30 microM) were effective in suppressing the amplitude of IA, whereas tetraethylammonium chloride (1 mM) and gabapentin (100 microM) had no effect on it. The time course for the inactivation of IA was changed to the biexponential process during cell exposure to LTG (100 microM). LTG (300 microM) could shift the steady-state inactivation of IA to a more negative membrane potential by approximately -10 mV, although it had no effect on the slope of the inactivation curve. Moreover, LTG (100 microM) produced a significant prolongation in the recovery of IA inactivation. Therefore in addition to the inhibition of voltage-dependent Na+ channels, LTG could interact with the A-type K+ channels to suppress the amplitude of IA. The blockade of IA by LTG does not simply reduce current magnitude, but alters current kinetics, suggesting a state-dependent blockade. LTG might have a higher affinity to the inactivated state than to the resting state of the IA channel. CONCLUSIONS: This study suggests that in hippocampal neurons, during exposure to LTG, the LTG-mediated inhibition of these K+ channels could be one of the ionic mechanisms underlying the increased neuronal excitability.     

白黎芦醇对GH3细胞增殖和PRL合成的影响

目的 探讨白黎芦醇对垂体腺瘤GH3细胞增殖和泌乳素合成的影响，及其对雌激素的拮抗作用。方法 在无血清无酚红的培养条件下，白黎芦醇单独或与雌二醇联合作用于GH3细胞，用MTT法测定细胞增殖，用免疫荧光法、RT-PCR和Western印迹法测定泌乳素的表达情况。结果 白黎芦醇对GH3细胞增殖具有刺激和抑制双相作用，呈时间一剂量依赖性。并且白黎芦醇使GH3细胞中PRL阳性细胞比例下降。同时，白黎芦醇抑制泌乳素的合成。白黎芦醇对雌二醇诱发的细胞增殖和泌乳素合成均有拮抗作用．但对泌乳素合成的拮抗作用较强，而雌二醇刺激细胞增殖作用较其诱发泌乳素合成作用强。结论 白黎芦醇对GH3细胞增殖和泌乳素合成均有抑制作用，从两方面发挥着抗肿瘤作用。     

氟维司群对泌乳素瘤GH3细胞系增殖和分泌的影响

目的探讨雌激素受体拮抗剂氟维司群对泌乳素腺瘤GH3细胞增殖和分泌泌乳素的影响。方法将GH3细胞分为对照组、不同浓度的氟维司群组（0．04、1、25、625nM）和雌二醇组。观察氟维司群和雌二醇对GH3细胞活力、泌乳素水平、凋亡以及转化生长因子-β3（Transforming growth factorβ3,TGF—β3）的影响。结果与对照组相比,雌二醇组GH3细胞活力明显增加（P〈0．01）,氟维司群25nM组和625nM组细胞活力分别下降35．3％和42．4％,差异显著（P〈0．01）。与对照组和雌二醇组相比,1nM组凋亡细胞增加,差异有统计学意义（P〈0．05）,25nM组和625nM组凋亡细胞数分别占总细胞数12．9％和17．3％．差异显著（P〈0．01）。与对照组相比,氟维司群能抑制泌乳素分泌,25nM组和625nM组分别下降62.3％和81．6％,差异佩著（P〈0．01）。蛋白印迹试验证实雌激素可抑制TGF—β3表达,随着氟维司群浓度增加,TGF-β3表达量逐渐上升。结论雌二醇可促进GH3细胞增殖和泌乳素分泌,而雌激素受体拮抗剂氟维司群能够有效抑制雌激素作用,期问有TGF—β3参与,为泌乳素瘤临床治疗提供新的药物选择。     

白藜芦醇抑制U251人胶质瘤细胞增殖及其相关机制的探讨

目的 探讨白藜芦醇（Res）对U251胶质瘤细胞增殖和侵袭的抑制作用及其机制。方法 将不同浓度Res作用于U251胶质瘤细胞系，相差显微镜下观察其形态的变化，MTT法检测其对细胞生长增殖的抑制作用，流式细胞术（FCM）检测其对细胞周期的影响，用蛋白印迹（Western blot）检测Res处理前后U251细胞表皮生长因子受体（EGFR）、p53、p21、CDK4、CyclinD1、Bcl-2及caspase-3的表达，免疫组化分析MMP9、NFKB、P-AKT及AKT2的表达。结果 U251细胞经Res处理后，细胞形态发生一定变化，U251胶质瘤细胞的增殖被抑制，呈浓度和时间依赖性，细胞周期被阻滞在S期，Western blot检测显示EGFR、CyclinD1、CDK4、Bcl-2的表达降低，p21、p53、caspase-3蛋白表达升高，免疫组化检测显示MMP9，NFKB、P-AKT及AKT2的表达降低。结论 Res有可能通过调节EGFR及p53信号通路而抑制U251胶质瘤细胞的增殖和侵袭，诱导肿瘤细胞凋亡。     

Inhibitory effect of calcium channel blockers on proliferation of human glioma cells in vitro

The effects of 2 specific calcium channel blockers, verapamil and nimodipine, on the proliferation of human glioma tumour cells were investigated in vitro. Tumour tissues for primary cell cultures were obtained bioptically from 3 patients with the histopathological diagnosis of glioblastoma. The [3H]-thymidine incorporation into glioma tumour cells DNA was used as a sensitive index of the cell proliferation. It was found that verapamil (10(-4)-10(-5) M) and nimodipine (10(-4)-10(-6) M) significantly inhibited the [3H]-thymidine uptake in a dose-related manner. The inhibitory effect of both calcium channel antagonists was reversed by simultaneous addition of calcium chloride (5 x 10(-3) M). These results indicate that verapamil and nimodipine may exert an antiproliferative effect on glioma cells growth acting through a blockade of specific voltage-dependent calcium channels.     

姜黄素诱导自噬抑制脑胶质瘤U87细胞增殖的研究

目的研究姜黄素对脑胶质瘤U87细胞增殖的抑制作用及机制。方法采用10、20、40、60、80μmol/L姜黄素分别处理U87细胞72h后,MTT法检测姜黄素对U87细胞增殖的影响。流式细胞术检测40μmol/L姜黄素处理前后U87细胞周期和凋亡变化。提取40μmol/L姜黄素处理前后不同时间点U87细胞总蛋白,Westernblot检测自噬相关蛋白LC3的表达。结果姜黄素呈剂量依赖性抑制U87细胞增殖(P0.05),半数抑制浓度(IC50)为42.44μmol/L。姜黄素诱导G2-M期细胞周期阻滞,实验组G2-M期细胞比例为(47.71±2.67)%,对照组为(17.96±0.88)%(P0.01);实验组细胞凋亡率为(3.93±0.82)%,对照组为(1.80±0.65)%,两组差异无统计学意义(P0.05)。姜黄素给药12、24、48h,LC3-Ⅱ/LC3-Ⅰ比值分别为(0.89±0.004)、(0.93±0.01)、(1.09±0.02),高于对照组(0.76±0.04)(P0.05);3-MA能减弱姜黄素对U87细胞增殖的抑制作用。结论姜黄素通过诱导自噬抑制脑胶质瘤U87细胞的增殖。     

大鼠脂肪干细胞定向分化为成骨细胞及体外增殖过程中地塞米松的抑制性干预

背景：不同浓度的地塞米松在体外诱导脂肪干细胞向成骨细胞分化过程中所起的作用是不同的,其作用机制尚不明确。 目的：验证脂肪干细胞向成骨细胞分化的能力,观察成骨细胞分化早期不同浓度地塞米松对脂肪干细胞体外增殖的抑制效果。 设计、时间及地点：细胞学体外观察,于2008-01/03在南方医科大学组织工程研究中心完成。 材料：5周龄雄性SD大鼠10只,由南方医科大学实验动物中心提供。地塞米松为Sigma公司产品。 方法：切取大鼠腹股沟皮下脂肪组织,用酶消化法分离培养脂肪干细胞,传至第3代后,加入条件培养液(含胎牛血清、维生素C、β-甘油磷酸钠、青霉素、链霉素的DMEM高糖完全培养基)进行体外预培养。设立2组：地塞米松组分别于细胞传代后第0,2,4天向培养基中加入10-6 mol/L地塞米松1 mL,空白对照组仅加入等量条件培养液。 主要观察指标：倒置显微镜下观察细胞生长及成骨分化情况。采用MTT比色法检测细胞增殖情况。 结果：①原代培养中贴壁细胞多数呈长梭形,少数呈小圆形或三角形,六七天后进行传代;传代后细胞生长速度较原代细胞明显增快,至第15代细胞仍未出现明显衰老现象;第3代细胞在加入地塞米松后逐渐呈均一的长梭形,随时间延长呈叠形多层排列,细胞外基质明显增多,并逐渐形成多个小结样结构。空白对照组细胞形态不一,部分细胞呈多边形或三角形,细胞外基质明显少于地塞米松组,罕见小结样结构。②在体外传代培养过程中,空白对照组脂肪干细胞能够保持持续分裂增殖的能力。与空白对照组比较,细胞传代培养后0,2 d加入地塞米松,干预6,8,10,12 d时细胞数量均明显下降(P < 0.05);传代培养后4 d加入地塞米松,干预6,8,10,12 d时细胞数量无明显变化(P > 0.05)。 结论：传代的脂肪干细胞经地塞米松处理后,细胞形态趋于成熟,生长速度减慢,可定向分化为成骨细胞。在向成骨细胞分化早期,地塞米松能够抑制脂肪干细胞的体外增殖。     

Phencyclidine selectively blocks the sustained voltage-dependent potassium conductance in PC12 cells

We investigated the effects of phencyclidine (PCP), a psychotomimetic dissociative anesthetic, and several related drugs on voltage-dependent K+ currents in PC12 cells, a neuron-like clonal cell line derived from a rat pheochromocytoma. Whole-cell voltage clamp recordings demonstrated two kinetically distinct voltage-dependent outward (K+) current components in these cells: a rapidly activating and inactivating component, IA, that was selectively eliminated by 4-aminopyridine (2 mM) and a slowly activating, minimally inactivating (sustained) component, IK, that was specifically blocked by tetraethylammonium (20 mM). PCP (1-100 microM) produced a dose-dependent blockade of both IK and IA, however, at low doses the drug selectively reduced IK with little effect on IA; the IC50s for blockade of IK and IA were 4 and 25 microM, respectively. The blockade of IK was voltage-dependent so that the degree of block decreased with increasing depolarization, indicating that the blocking mechanism is likely one in which the positively charged PCP molecule is drawn into the channel pore. Several PCP related drugs also suppressed IK. Thienyl-PCP (TCP), a drug that is behaviorally more potent than PCP, partially blocked IK at low doses (31% at 1 microM), but even at high doses (25 microM) the degree of block was never as great as that produced by PCP. The optically active PCP congeners (+)-PCMP (1-(1-phenylcyclohexyl)-3-methyl-piperidine) and dexoxadrol were also potent blockers of IK. However, in contrast to the stereospecificity these compounds demonstrate in binding to high-affinity PCP receptors and in eliciting PCP-like behavioral responses, their enantiomers (-)-PCMP and levoxadrol showed similar potencies as the parent compounds in blocking IK. These results demonstrate that PCP and related drugs are powerful, selective blockers of IK in PC12 cells. The structure-activity studies indicate that this effect occurs at a site that is pharmacologically distinct from the behaviorally relevant PCP receptor. Blockade of K+ channels is unlikely to be responsible for the psychotomimetic or anti-convulsant properties of PCP, but could account for the convulsant potential of the drug.     

白藜芦醇对垂体腺瘤GH3细胞增殖和PRL合成的拮抗作用

目的探讨白藜芦醇对雌激素诱发的垂体腺瘤细胞系（GH3细胞）增殖和泌乳素（PRL）合成的拮抗作用。方法在无血清无酚红的条件下，将雌二醇（E2）单独或与白藜芦醇联合作用于培养的GH3细胞，用甲基噻唑基四唑（MTT）比色分析法测定细胞生长，用免疫荧光及Western Blot检测GH3细胞增殖和PRL的表达情况。结果白藜芦醇对雌二醇诱发的细胞增殖和PRL合成均有拮抗作用，其中对PRL合成的拮抗作用较强。结论白藜芦醇对雌二醇诱发的细胞增殖和PRL合成均有拮抗作用，从而起到抗肿瘤的作用。     

microRNA-613调控CDK14来抑制老年胶质瘤患者瘤细胞的增殖和侵袭作用

目的 探讨microRNA-613调控细胞周期蛋白依赖性激酶14(CDK14)通路来抑制老年胶质瘤患者瘤细胞增殖和侵袭的机制。方法 购自上海北诺生物科技有限公司的人脑胶质瘤细胞株U251共24株,分为shNC组、shmicroRNA-613组、Vector组、microRNA-613组,每组各6株; Western Blotting法和qRT-PCR法检测敲减microRNA-613和过表达microRNA-613后的人脑胶质瘤细胞株U251中CDK14蛋白表达水平,CCK-8细胞增殖实验、Transwell小室实验验证敲除microRNA-613和过表达microRNA-613后U251细胞的增殖、侵袭能力。结果 人胶质瘤细胞株U251敲减microRNA-613后CDK14蛋白表达增加(P<0.05); 人胶质瘤细胞株U251过表达microRNA-613后CDK14蛋白表达减少(P<0.05); 转染第24、36、48 h microRNA-613组U251细胞增殖率P<0.05); microRNA-613组U251细胞侵袭能力>Vector组,shNC组>shmicroRNA-613组(P<0.05)。结论 microRNA-613可通过调控CDK14信号转导通路来抑制人脑胶质瘤细胞U251增殖、转移。     

Halothane inhibits two components of calcium current in clonal (GH3) pituitary cells.

The effect of halothane on isolated calcium (Ca2+) current of clonal (GH3) pituitary cells was investigated using standard whole-cell clamp techniques at room temperature. Halothane (0.1-5.0 mM) reversibly reduced both the low-threshold, transient [low-voltage-activated (LVA)] component and the high-threshold [high-voltage-activated (HVA)] component of Ca2+ current. Halothane had little effect on the voltage dependence of activation or inactivation of either component of Ca2+ current. Inhibition of the peak high-threshold Ca2+ current was half-maximal at about 0.8 mM halothane, with maximal inhibition (100%) occurring with 5 mM halothane. When measured at the end of a 190-msec command step, half-maximal reduction of high-threshold current occurred at less than 0.5 mM halothane. The low-threshold transient current was less sensitive to halothane, with half-maximal inhibition of peak transient current activated at -30 mV occurring at approximately 1.3 mM. The effect of halothane on the HVA current was apparently not mediated by changes in intracellular Ca2+ concentration. The ability of halothane to inhibit Ca2+ current was unaffected by either the inclusion of the rapid Ca2+ buffer 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA) in the recording pipette or exposure of the cell to 10 mM caffeine. To assess the selectivity of the effect of halothane, the actions of halothane on two components of voltage-activated potassium (K+) current observed in the absence of extracellular Ca2+ and on voltage-dependent sodium (Na+) current were also examined. Halothane had no effect on the voltage-dependent, inactivating K+ current of GH3 cells at concentrations up to 1.2 mM. In contrast, the non-inactivating K+ current, though less sensitive to halothane than either Ca2+ current, was reduced by about 40% by 1.2 mM halothane at +20 mV. Peak Na+ current was also blocked by halothane, but 50% block required around 2.6 mM halothane with little effect at 1.6 mM. Reduction of Na+ current was associated with a substantial negative shift in the steady-state inactivation curve. Although the results indicate that a number of voltage-dependent ionic currents are sensitive to halothane, both components of Ca2+ current exhibit a greater sensitivity to halothane than any of three other voltage-dependent currents in GH3 cells. These results show that GH3 cell Ca2+ currents are selectively inhibited by clinically appropriate concentrations of halothane and that the reduction of Ca2+ current can account for the inhibition by halothane of TRH- or KCl-induced prolactin secretion in GH3 cells.     

hTERT反义cDNA对人脑胶质瘤细胞的抑制作用

目的探讨人端粒酶催化亚基(hTERT)反义cDNA(pAdeasy-hTERT)在体外对胶质瘤细胞生长的抑制作用。方法将腺病毒介导的pAdeasy-hTERT作用于人胶质瘤细胞系U251,用MTT法检测细胞存活率、端粒酶重复序列扩增法测定端粒酶活性、Westem杂交鉴定hTERT蛋白的表达、RT-PCR法检测hTERT cDNA水平、PCNA观察肿瘤细胞的凋亡情况以及用流式细胞仪对转染后肿瘤细胞的周期进行分析。结果pAdeasy-hTERT在体外明显抑制肿瘤细胞生长,降低端粒酶活性,抑制hTERT表达。结论pAdeasy-hTERT显著抑制人胶质瘤细胞生长,可成为恶性胶质瘤基因治疗的靶基因。     

Cisplatin blocks voltage-dependent calcium current in dissociated outer hair cells of guinea-pig cochlea

The effect of the ototoxic molecule cisplatin (cis-DDP) on the voltage-dependent Ca²⁺ channel in dissociated outer hair cells (OHCs) of guinea-pig cochlea was investigated using a whole-cell pathch-clamp technique. Cis-DDP had antagonistic effect on the Ca²⁺ channel and reversibly suppressed the Ca²⁺ current in a concentration-dependent manner. These results suggested that one of the ototoxic mechanisms of cis-DDP is involved in the inhibition of the Ca²⁺ channel in OHCs.     

蒿甲醚对C6胶质瘤细胞的抑制作用

目的 研究蒿甲醚对大鼠C6胶质瘤细胞的抑制作用.方法 C6胶质瘤细胞经培养后,按是否加入蒿甲醚分为实验组和对照组,均采用四甲基偶氮唑盐(MTT)法、流式细胞技术(FCM)及Hoechst33258荧光染色法检测细胞凋亡情况.结果 MTT法检测显示:24、48、72h3个时间组蒿甲醚对C6胶质瘤细胞的半数抑制浓度(IC50)分别为(195.08±3.27) μmol/L、(119.64±4.06) μmol/L、(87.84±0.93) μmol/L.FCM法检测显示:24、48、72 h3个时间组C6胶质瘤细胞凋亡率分别为:7.95％、22.01％、31.22％;且G0-G1期细胞比例增加,S期和G2-M期细胞比例降低.荧光染色显示:实验组细胞内出现凋亡小体;而对照组细胞呈弥散均匀荧光.结论 蒿甲醚能抑制C6胶质瘤细胞生长,且其抑制作用呈现时间依赖性和浓度依赖性;蒿甲醚能干扰C6胶质瘤细胞的细胞周期,可将其阻滞在G0-G1期并诱导其凋亡.     

AG490阻断STAT3信号通路对人胶质瘤细胞增殖和周期的抑制作用

目的 探讨AG490阻断STAT3信号通路对人胶质瘤细胞增殖和细胞周期的影响.方法 用不同浓度的AG490作用于体外培养的人胶质瘤细胞株U87、U251;用免疫荧光细胞化学染色观察肿瘤细胞STAT3和激活态p-STAT3的表达;Western blot验证AG490对STAT3信号通路的阻断情况;Sulforhodamine B染色观察肿瘤细胞增殖的改变;流式细胞技术分析细胞周期的变化. 结果 STAT3蛋白在胶质瘤细胞胞浆中表达,而P-STAT3则在细胞核中表达.AG490作用胶质瘤细胞后可使p-STAT3表达下降,而STAT3表达不受影响.AG490阻断STAT3信号通路后,胶质瘤细胞的增殖受到显著抑制,该抑制作用与剂量及时间存在一定关系.AG490作用后胶质瘤的细胞周期出现阻滞.结论 应用AG490阻断STAT3通路能够导致胶质瘤细胞增殖的抑制和细胞周期的阻滞.针对STAT3信号通路的研究可能为胶质瘤的治疗提供更加有效的方法.     

D2L,D2S,and D3 dopamine receptors stably transfected into NG108-15 cells couple to a voltage-dependent potassium current via distinct G protein mechanisms

The D₂-like dopamine (DA) receptor family has continued to expand and now includes the D₂-short (D_2S) and D₂-long (D_2L) receptor isoforms and the D₃ and D₄ receptors. The D₂ receptor isoforms differ in length by 29 amino acids within the third cytoplasmic loop, a region of the receptor believed to be important for G protein coupling. This observation has led to the hypothesis that the two isoforms of the D₂ receptor may utilize different signal transduction pathways when present in the same cell. The D₂ and D₃ receptors, although mostly different, show some common amino acid sequences within the third cytoplasmic loop. Thus, it is possible that the D₂ and D₃ receptors may employ similar signal transduction pathways. To test these hypotheses directly, NG108-15 neuroblastoma-glioma hybrid cells were stably transfected to express either the D_2S, D_2L, or D₃ DA receptors. All transfected but not untransfected NG108-15 cells demonstrated a dose-dependent reduction in the peak whole-cell potassium (K⁺) current in response to receptor activation by DA or the DA receptor agonists quinpirole (QUIN) and apomorphine (APO). The modulation of K⁺ current by D_2S receptor stimulation was prevented by pretreatment of the cells with cholera toxin (20 μg/ml for 18 h), whereas pertussis toxin pretreatment (500 ng/ml for 4 h) completely blocked the effects of D_2L and D₃ receptor activation. These observations suggest that the signal transduction mechanisms involved in coupling the two isoforms of the D₂ receptor to the K⁺ current are different, whereas the D_2L and D₃ receptor coupling mechanisms may be similar. In direct support of this hypothesis, it was observed that the intracellular application of a polyclonal antibody that is specific for the G_0α subunit completely blocked the ability of D_2L and D₃ receptors to modulate outward K⁺ currents. In contrast, the D_2S-mediated modulation of K₊ currents was blocked by intracellular application of an antibody recognizing G_Sα but not G_0α. These findings demonstrate that D_2S and D_2L receptors are able to couple to a common effector in a cell via two G protein pathways. © 1996 Wiley-Liss, Inc.